FOR the past several months, I’ve been wrapping up lengthy interviews with Washington counterterrorism officials with a fundamental question: “Do you know the difference between a Sunni and a Shiite?”

A “gotcha” question? Perhaps. But if knowing your enemy is the most basic rule of war, I don’t think it’s out of bounds. And as I quickly explain to my subjects, I’m not looking for theological explanations, just the basics: Who’s on what side today, and what does each want?

After all, wouldn’t British counterterrorism officials responsible for Northern Ireland know the difference between Catholics and Protestants? In a remotely similar but far more lethal vein, the 1,400-year Sunni-Shiite rivalry is playing out in the streets of Baghdad, raising the specter of a breakup of Iraq into antagonistic states, one backed by Shiite Iran and the other by Saudi Arabia and other Sunni states.

A complete collapse in Iraq could provide a haven for Al Qaeda operatives within striking distance of Israel, even Europe. And the nature of the threat from Iran, a potential nuclear power with protégés in the Gulf states, northern Saudi Arabia, Lebanon and the Palestinian territories, is entirely different from that of Al Qaeda. It seems silly to have to argue that officials responsible for counterterrorism should be able to recognize opportunities for pitting these rivals against each other.

But so far, most American officials I’ve interviewed don’t have a clue. That includes not just intelligence and law enforcement officials, but also members of Congress who have important roles overseeing our spy agencies. How can they do their jobs without knowing the basics?

My curiosity about our policymakers’ grasp of Islam’s two major branches was piqued in 2005, when Jon Stewart and other TV comedians made hash out of depositions, taken in a whistleblower case, in which top F.B.I. officials drew blanks when asked basic questions about Islam. One of the bemused officials was Gary Bald, then the bureau’s counterterrorism chief. Such expertise, Mr. Bald maintained, wasn’t as important as being a good manager.

A few months later, I asked the F.B.I.’s spokesman, John Miller, about Mr. Bald’s comments. “A leader needs to drive the organization forward,” Mr. Miller told me. “If he is the executive in a counterterrorism operation in the post-9/11 world, he does not need to memorize the collected statements of Osama bin Laden, or be able to read Urdu to be effective. … Playing ‘Islamic Trivial Pursuit’ was a cheap shot for the lawyers and a cheaper shot for the journalist. It’s just a gimmick.”

Of course, I hadn’t asked about reading Urdu or Mr. bin Laden’s writings.

A few weeks ago, I took the F.B.I.’s temperature again. At the end of a long interview, I asked Willie Hulon, chief of the bureau’s new national security branch, whether he thought that it was important for a man in his position to know the difference between Sunnis and Shiites. “Yes, sure, it’s right to know the difference,” he said. “It’s important to know who your targets are.”

That was a big advance over 2005. So next I asked him if he could tell me the difference. He was flummoxed. “The basics goes back to their beliefs and who they were following,” he said. “And the conflicts between the Sunnis and the Shia and the difference between who they were following.”

O.K., I asked, trying to help, what about today? Which one is Iran — Sunni or Shiite? He thought for a second. “Iran and Hezbollah,” I prompted. “Which are they?”

He took a stab: “Sunni.”

Wrong.

Al Qaeda? “Sunni.”

Right.

AND to his credit, Mr. Hulon, a distinguished agent who is up nights worrying about Al Qaeda while we safely sleep, did at least know that the vicious struggle between Islam’s Abel and Cain was driving Iraq into civil war. But then we pay him to know things like that, the same as some members of Congress.

Take Representative Terry Everett, a seven-term Alabama Republican who is vice chairman of the House intelligence subcommittee on technical and tactical intelligence.

“Do you know the difference between a Sunni and a Shiite?” I asked him a few weeks ago.

Mr. Everett responded with a low chuckle. He thought for a moment: “One’s in one location, another’s in another location. No, to be honest with you, I don’t know. I thought it was differences in their religion, different families or something.”

To his credit, he asked me to explain the differences. I told him briefly about the schism that developed after the death of the Prophet Muhammad, and how Iraq and Iran are majority Shiite nations while the rest of the Muslim world is mostly Sunni. “Now that you’ve explained it to me,” he replied, “what occurs to me is that it makes what we’re doing over there extremely difficult, not only in Iraq but that whole area.”

Representative Jo Ann Davis, a Virginia Republican who heads a House intelligence subcommittee charged with overseeing the C.I.A.’s performance in recruiting Islamic spies and analyzing information, was similarly dumbfounded when I asked her if she knew the difference between Sunnis and Shiites.

“Do I?” she asked me. A look of concentration came over her face. “You know, I should.” She took a stab at it: “It’s a difference in their fundamental religious beliefs. The Sunni are more radical than the Shia. Or vice versa. But I think it’s the Sunnis who’re more radical than the Shia.”

Did she know which branch Al Qaeda’s leaders follow?

“Al Qaeda is the one that’s most radical, so I think they’re Sunni,” she replied. “I may be wrong, but I think that’s right.”

Did she think that it was important, I asked, for members of Congress charged with oversight of the intelligence agencies, to know the answer to such questions, so they can cut through officials’ puffery when they came up to the Hill?

“Oh, I think it’s very important,” said Ms. Davis, “because Al Qaeda’s whole reason for being is based on their beliefs. And you’ve got to understand, and to know your enemy.”

It’s not all so grimly humorous. Some agency officials and members of Congress have easily handled my “gotcha” question. But as I keep asking it around Capitol Hill and the agencies, I get more and more blank stares. Too many officials in charge of the war on terrorism just don’t care to learn much, if anything, about the enemy we’re fighting. And that’s enough to keep anybody up at night.

Jeff Stein is the national security editor at Congressional Quarterly.